This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application OPTICAL WAVEGUIDE filed with the Korean Industrial Property Office on Apr. 19, 1999 and there duly assigned Serial No. 13807/1999.
1. Field of the Invention
The present invention relates to an optical waveguide, and more particularly, to an optical waveguide formed of a variable refractive index polyimide to give a great difference in the refractive index between core and cladding layers.
2. Description of the Related Art
The manufacture of optical waveguide devices utilizing techniques learned from semiconductor or micro mechanical systems (MEMS) manufacture has recently become commonplace. A planar waveguide technique for forming an optical waveguide device on a planar substrate has been introduced. Also, research into greater integration of optical waveguide devices is continuing to increase.
In a method for manufacturing a common optical waveguide device, an undercladding layer and a core layer are sequentially formed on a substrate. Then, a photoresist is deposited over the core layer and patterned into a photoresist pattern via exposing and developing procedures.
The core layer is etched into a predetermined pattern using the photoresist pattern as an etching mask, and an overcladding layer is formed thereon, resulting in a complete optical waveguide device. The cladding and core layers are formed by spin coating with silica or polymer having a different refractive index for the cladding and core layers.
In the case of using silica as a material for core and cladding layers, the difference in refractive index can be made up to 0.75%. However, the use of silica does not allow for decreasing the size of the optical waveguide, thereby making the production of a subminiature passive device for optical communications difficult.
A possible solution might be to use a polymer such as polyimide as a material for core and cladding layers, the fluorine or chlorine content within polyimide molecule being adjusted to determine the difference in refractive index between core and cladding layers, and in turn manufacture a larger optical waveguide, with reduced optical absorption loss.
However, known polyimides are not satisfactory in varying the difference in the refractive index between core and cladding layers as needed for such a device.
Therefore, it is an object of the present invention to provide an improved optical waveguide.
It is a further object of the invention to provide an improved subminiature optical waveguide.
It is a yet further object of the invention to provide an optical waveguide with the refractive index difference between the core and cladding easily controllable within a large range.
A still further object of the invention is to provide an optical waveguide device with greater refractive index difference than can be obtained using silica in the waveguide.
The objects of the present invention achieved by an optical waveguide comprising a core layer formed of a polymer, and a cladding layer placed proximate to the core layer, the cladding layer being formed of a polymer having a refractive index smaller than the refractive index of the polymer for the core layer,
wherein the polymers for the core and cladding layers are selected from the copolymers having the formula (1) 
where X is 
Y is 
n is a mole fraction in the range of 0.05xe2x89xa6n less than 1.